map

Applies a given project function to each value emitted by the source Observable, and emits the resulting values as an Observable.

map<T, R>(project: (value: T, index: number) => R, thisArg?: any): OperatorFunction<T, R>

Parameters

project	The function to apply to each value emitted by the source Observable. The index parameter is the number i for the i-th emission that has happened since the subscription, starting from the number 0.
thisArg	Optional. Default is undefined. An optional argument to define what this is in the project function.

Returns

OperatorFunction<T, R>: A function that returns an Observable that emits the values from the source Observable transformed by the given project function.

Description

Like Array.prototype.map(), it passes each source value through a transformation function to get corresponding output values.

Similar to the well known Array.prototype.map function, this operator applies a projection to each value and emits that projection in the output Observable.

Example

Map every click to the clientX position of that click

import { fromEvent } from 'rxjs';
import { map } from 'rxjs/operators';

const clicks = fromEvent(document, 'click');
const positions = clicks.pipe(map(ev => ev.clientX));
positions.subscribe(x => console.log(x));

See Also

• mapTo
• pluck